This study is for patients older than 12 who have been diagnosed with high-risk leukemia and for whom an unrelated bone marrow transplant is planned. We plan to enroll 10 patients on the study, over a 1-year period from the opening of the trial. Of these ten patients, at least five will be pediatric patients; the other five may be from adult patients taken care of by Winship Cancer Center physicians. All clinical study coordination and biologic studies will be performed by CHOA personnel.